Bulletins issued by the U.S. Occupational Safety and Health Administration (OSHA) have advised field personnel in petroleum refineries and in chemical plants of the potential safety and health risks posed by hydrofluoric acid (HF) used in HF alkylation units and in other services. These bulletins have also presented control measures to reduce workers' exposure.
In recent years, the petroleum refining industry has placed an increasing emphasis on safety when using HF in petroleum refineries. Refineries use the acid in a process called “alkylation,” for producing high-octane gasoline. Hydrofluoric acid is hazardous and corrosive and, if accidently released, can form a vapor cloud. If the vapor cloud is sufficiently concentrated, it can be toxic. OSHA also notes that there have been a number of accidental releases of this acid from alkylation units at major petroleum refineries in the United States.
Pure hydrogen fluoride is a clear, colorless, corrosive liquid that has roughly the same weight as water (comparing equal volumes). It boils at 67° F. and can form a vapor cloud if released to the atmosphere. It has a sharp, penetrating odor that humans can detect at very low concentrations (0.04-0.13 ppm2) in the air.
To protect against adverse effects from exposure to hydrofluoric acid in the workplace, OSHA has established a permissible exposure limit (PEL) of 3 ppm averaged over an eight-hour work shift. The National Institute for Occupational Safety and Health has established an “Immediately Dangerous to Life or Health” (IDLH) concentration level for HF of 30 ppm3.
Any contact with HF liquid or vapor cats produce serious, painful chemical burns, sometimes with delayed onset and hypocalcemia. The vapor can be extremely irritating to the eyes, skin and respiratory tract. Short-term exposure at high concentrations can cause serious health effects or death due to extensive respiratory damage.
As with other refinery processes, the primary exposure control method used in HF alkylation units is to contain of all process substances within the unit equipment (i.e., vessels, piping, and pumps). The greatest potential for exposure occurs: during process stream sampling; when unloading the HF from trucks; as a result of process leaks (fugitive emissions); as a result of equipment failures (e.g., pump seals); and during equipment maintenance.
Commonly, vats containing soda ash solutions have been used for neutralizing any contaminated equipment which must be removed from the HF alkylation unit for maintenance, replacement or disposal. However, the vats currently used in the art are not well suited for effectively and safely neutralizing valves which have been used in HF service or have been used for delivering other toxic or harmful fluids.
Consequently, a need exists for an improved tank assembly, system, and method for neutralizing valves which have been used in HF service or in other toxic or harmful services. Moreover, a need particularly exists for an improved neutralization or decontamination tank assembly, system, and method wherein a contaminated valve can be fully submerged in the treatment fluid and held securely in place such that, while the valve is held below the liquid level, the field personnel can easily open the valve, remove any packing therein, and loosen, cycle, or otherwise expose all of the components of the valve for thorough neutralization and decontamination, while at the same time helping to protect the field personnel from exposure.